Study On The Resistance Of SO₂ Of Fe-Mn Based Catalysts For Selective Catalytic Reduction Of NO_x With NH₃ At Low-temperature

As we all know NO_x is a major component of photochemical smog,that has an important effect on humans health,production and life and even the natural environment.Thus,in our country,several regulations had been put into force in the"12th Five-Year"period in order to eliminate NOx.Selective catalytic reduction?SCR?technology has been most widely used in the field of flue gas denitrification.How to achieve the high conversion efficiency of NOx under 150?has been concerned by academic circles for long time.At present,SCR technology is not widely used in commercial areas.The main obstacle was poor activitity at low temperature,poor sulfur resistance,poor reaction mechanism and so on.The Mn-Fe/TiO₂catalyst was preparaed by sol-gel method,the factors were investigated to optimize its performance,and a series of manganese catalysts with different doping elements were obtained.The catalysts were characterizated by using X-ray diffraction,BET,In Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy,Temperature Programmed Reduction and Temperature Programmed Desorption.Finally,the SCR reaction mechanism was proposed based on the results of DRIFTs.Firstly,the relationship between SCR activity of Mn-Fe/TiO₂ catalyst and operating paramcter was investigated.Mn-Fe/TiO₂ catalyst was prepared by sol-gel method and the effect of Fe loading on the performance of the catalyst was investigated.It was found that Mn-Fe/TiO₂ had relatively higher SCR acivity at low-temperature when the water content is8%,the oxygen content is 4%,the space velocity is 30000 h^-1,the load molar ratio of active component between Fe and Ti is 0.24 and the calcined temperature is 400?.The activity of the catalyst increased with the increase of Fe loading,but the sulfur resistance decreased gradually.The oxides of Fe and Mn were distributed on the surface of anatase TiO₂ carrier in amorphous state.The oxygen storage capacity and the surface acidity of the Mn-Fe/Ti O₂catalyst were improved by the introduction of Fe,which would be beneficial to the adsoroption of NH₃ and its activitation.At the same time,it was found that enhanced the calcination temperature can improve the activity of SCR catalyst at low temperature.The crystallinity of anatase TiO₂ was increased,surface area and pore volume were decreased,the catalyst redox and adsorption ability were decreased with the increase of calcination temperature.Secondly,The SCR reaction mechanism of Mn-Fe/TiO₂ catalyst were performed by FTIR investigations.The results showed that the NH₃ adsorbed on the Lewis acid sites on the surface of catalyst and formed coordination state NH₃,and the NH₄⁺was formed on the Br?nsted.The reaction between NH₃ of the L acid sites on the catalyst surface and nitrite species of the B acid sites,indicating that there are two kinds of reaction mechanism of L-H and E-R on the catalyst surface.The reaction between NH₃ with coordination state and nitrite to complete the SCR reaction when the SCR reaction occurs.Finally,on the basis of this study,the Mn/TiO₂ was modified by doping Ce,Sm,Fe,Cu and Ni metal elements,it was found that Fe and Ni doping can reduce the crystallinity of TiO₂carrier and improve the catalytic redox properties through the characterization results of experiment and test.In addition,the sulfur resistance of manganese catalysts were examined systemly,the process of catalyst sulfuric acid was inhibited effectively by the surface doping of Ce and Sm,but some insoluble sulfates or ammonium sulfate substances generated on catalysts surface,result that it can not reach the 100%original removal rate of NO_x after washing.